The present invention, generally, relates to a projected-image visual system as used in a simulator and, more particularly, relates to a digital distortion-correcting circuit for projecting a flat image on a curved screen in such a visual system.
Visual scenes that are viewed in the real world are simulated by projecting images from a video source onto a screen.
For large fields of view (FOV's), generally the screen surface is curved with the projection optics projecting over a wide angle.
The video output, which usually consists of a database transformed onto a flat image plane, must be processed by a suitable electronic system before it is projected onto a curved screen surface.
It is this processing function that is required of the electronic system that the present invention is concerned. This processing function is termed "mapping" in the art.
"Mapping" is defined as changing the output video elements from the image source such that the inherent time relationships of the elements is not equivalent to the resultant spatial relationships on the projector plane.
"Mapping" is required in the electronic system for three basic reasons, including (1) nominal design, (2) manufacturing tolerances, and (3) drifts. There are elements of a nominal system which require "mapping". The digital image source compensates for the fact that both the projection and the viewing point are not at the same center.
However, the image source can only produce "mapping" which is suitable for projection on a flat screen by a special-purpose projector. In addition to the mapping requirement identified above, the special-purpose projector has some sweep non-linearity inherent in its nominal design that requires some "mapping" correction.
Several elements of the visual system are subject to manufacturing tolerances to a sufficient degree that an alignable "mapping" corrector must be utilized to reduce distortion to acceptable levels. Examples of these include projector sweep non-linearities, wide-angle lens system geometric distortion, and spherical screen radius.
The "mapping" that is required in the environment described above is provided by the distortion-correcting circuit of the present invention.